1. Field of the Invention
The invention relates to an LED lamp and method of manufacture, and more particularly to a structure of the so-called white LED lamp that includes an LED chip capable of emitting a blue light. A fluorescent material can be disposed on or adjacent to an optical path of the light emitted from the LED chip to emit a yellow light when excited by the blue light. The blue light from the LED chip and the yellow light from the fluorescent material can be mixed to yield a white light, which can then be externally emitted.
2. Description of the Related Art
An LED chip capable of emitting a blue light, and a fluorescent material that is operative to emit a yellow light when excited by the blue light from the LED chip, are employed in the art to yield a white light. In this case, the LED chip is die-mounted in a recessed cavity provided in a base, followed by necessary wiring of gold wires, for example. Then, it is molded in a transparent resin with a certain depth to form a transparent spacer. Further, a resin that contains a fluorescent material uniformly dispersed therein is poured with a uniform thickness onto the transparent spacer to form a second layer that contains the fluorescent material in an appropriate direction.
Thus, the blue light emitted from the LED chip, though it may advance in any direction, transmits through the second layer which has an almost uniform thickness. Therefore, substantially all portions of the second layer have almost similar ratios in the amount of light which transmits through the second layer as the blue light as compared to the amount of light which is converted at the second layer into a yellow light. Accordingly, the entire surface of the second layer can be viewed as white. This is advantageous to prevent variations in color and achieve the high-quality emission of light (see JP-A 2000-77723 which corresponds to U.S. Pat. No. 5,959,316).
In recent years, the demand for the so-called white LED lamp has increased as a tendency for its use in a portable lighting device, for example, has grown, and accordingly requires a larger power. Therefore, upsizing the LED chip and increasing the drive power are promoted. Thus, the density of the blue light, which impinges on and excites the fluorescent material in the second layer, has tended to be further improved.
The fluorescent material can not convert all the impinged blue light into yellow light, but has the tendency to lower the wavelength conversion efficiency as the density of the impinging light increases. The remaining energy not converted into a certain color is turned into heat. In this case, the fluorescent material has a general temperature characteristic that lowers the wavelength conversion efficiency in higher temperatures.
In the LED lamp with the conventional structure as disclosed in JP-A 2000-77723, upsizing the LED chip and increasing the drive power supplied to the LED chip are performed to increase the density of the light beam from the LED chip that impinges on the fluorescent. As the density of the light beam is increased, in other words, the power consumed in the LED chip is increased, the amount of light may saturate and therefore become phenomenally lower. In addition, generation of heat can not be neglected when a number of LED lamps are employed.